Multi-Drive Powertrain Configurations for Electric and Hybrid Vehicles

Over the last fifteen years, the automotive market experienced a renewed interest towards electric and hybrid cars which, in turn, pushed the mayor manufacturers to increase investments in this sector, while also allowing new players to enter the market with innovative solutions. This gave rise to traction systems significantly different from the traditional ones, also from the conceptual point of view. An example is the powertrain “splitting”, namely the subdivision of the propulsive power between several subsystems more or less independent from each other. Literature shows that this solution can bring significant benefits, both under the powertrain point of view and the vehicle as a whole. Since the tractive effort is divided among several sub-components, these can be sized to a lower rated power, be more compact and easier to accommodate in the vehicle. Furthermore, the power splitting brings to higher reliability and enhanced vehicle dynamic performance. Eventually, for selected power ranges, it has been found possible to supply the traction drives at ultra-low voltage, i.e. 48 V, still achieving interesting performances, with clear benefits in terms of safety and simplicity. The research activity found practical application in the “AMBER-ULV” FP7 European project, for which a two-motor, two-axle, two-batteries traction system with a centralized control unit was developed. A model of the high-level control algorithm was conceived and run on the ECU thanks to model-based automatic code generation with integration of a stability control algorithm externally provided. The research activity also included the design of the traction drives, the low-level software and their integration on the vehicle. The prototype was also widely tested in several conditions in order to demonstrate the validity of the design process and choices.